1. Field of the Invention
The present invention relates to a color cathode-ray tube having a shadow mask.
This invention relates to a color liquid-crystal display device with a color filter layer, and more particularly to a half-transmission color liquid-crystal display device which has a backlight and a reflecting plate for reflecting external light and can function as a reflective/transmission color liquid-crystal display device.
2. Description of the Related Art
In recent years, liquid-crystal display devices have been applied in various forms, including the displays of notebook-type computers, monitors, car navigation systems, function electronic calculators, and medium- and small-sized TV sets. Since the reflective liquid-crystal display device requires no backlight, the application of the display device to the displays on portable devices, such as mobile PCs, has been studied because of the advantages of less power consumption, thinness, and lightness.
Like a sheet of paper, a conventional reflective liquid-crystal display device displays images with the help of external light. Therefore, when the device is used in a dark environment, the display screen becomes dark, which makes it difficult to view the image on the screen. Particularly in the darkness, it cannot be used at all.
To overcome this problem, a half-transmission liquid-crystal display device has been developed which includes a half-transmission reflecting plate, such as a half mirror, and a backlight so that it may function as a transmission liquid-crystal display device using the backlight in a dark environment.
In addition, a half-transmission liquid-crystal display device has been studied which has pinholes made in the reflecting plate in such a manner that the pinholes correspond to the individual pixels and which has microlenses provided for the pixels in a one-to-one ratio. When this liquid-crystal display device is used as a reflective liquid-crystal display device, the brightness of the screen display decreases only as much as there are pinholes in comparison with an ordinary reflection liquid-crystal display device. When it is used as a transmission liquid-crystal display device, the brightness of the display screen similar to that of an ordinary transmission liquid-crystal display device can be obtained by gathering the light emitted from the backlight with the microlenses and allowing the rays of the light to pass through the pinholes. This improves the brightness of the aforementioned half-transmission liquid-crystal display device.
Use of a color filter layer enables such a half-transmission liquid-crystal display device to provide a color display. Specifically, a conventional half-transmission color liquid-crystal display device is constructed by laying a polarizing plate, a front substrate, a color filter layer, driving electrodes, a liquid-crystal layer, a back substrate, a half reflecting plate, and a backlight one on top of another in that order. The color filter layer is provided in front of the reflecting plate, that is, on the side of the observer.
Therefore, when the liquid-crystal display device is used as the reflective type, external light entered through the front substrate passes through the color filter layer and liquid-crystal layer, then is reflected by the reflecting plate, and passes through the liquid-crystal layer and color filter layer again, and thereafter goes outside. Namely, the light passes through the color filter twice. Therefore, like an ordinary reflective color liquid-crystal display device, the color filter layer used has such a spectral characteristic as provides the desired coloring when light has passed through the color filter layer twice.
When the device functions as a reflective liquid-crystal display device, the light source is external light and the intensity of the light cannot be controlled freely. Additionally, when the polarizing plate is used, the transmittance of the entire liquid crystal element is insufficient. Therefore, the spectral characteristic of the color filter layer has a minimum transmittance of 0.1 or more, with the maximum transmittance being 1. Consequently, the spectral characteristic of such a color filter layer has been designed to provide so low color density that only one pass of light through the color filter layer cannot effect sufficient coloring.
Actually, the color filter layer has such a spectral characteristic as provides lower color density than that of the spectral characteristic of a RGB color filter layer used in a conventional transmission liquid-crystal display device, even after light has passed through the color filter layer twice.
On the other hand, when the half-transmission liquid-crystal display device is used as the transmission type, light emitted from the backlight passes through the color filter layer only once. As a result, the spectral characteristic of the display when the device functions as the transmission type, is the spectral characteristic when light has passed through the color filter layer once, or the spectral characteristic of the color filter layer itself. As a result, use of the aforementioned color filter layer provides very low color density.
Conversely, in a case where the half-transmission liquid-crystal display device uses a color filter layer whose spectral characteristic is the same as that of a color filter used in a conventional transmission liquid-crystal display device, when the device function as the reflective type, the brightness of the display is lacking seriously.
As described above, with the conventional half-transmission color liquid-crystal display device, the device provides only one of the following optical characteristics: when the device functions as the reflective type, the brightness of the display decreases seriously, or when the device functions as the transmission type, the color density of the display gets lower significantly.
The present invention is contrived in consideration of the above circumstances and its object is to provide a half-transmission liquid-crystal display device capable of making a sufficiently bright display with sufficient color density even when the device functions as the reflective type or as the transmission type.
The foregoing object is accomplished by providing a liquid-crystal display device comprising: a front substrate and a back substrate which are arranged to face each other and on an inner surface of each of which a liquid-crystal driving electrode is provided; a liquid-crystal layer sandwiched between the front substrate and the back substrate, for modulating the phase of incident light according to an applied voltage; a phase difference plate and a polarizing plate with a polarizing axis which are provided in that order on an outer surface of one of the front and back substrates; a half-transmission, half-reflection layer formed on the other substrate; a color filter layer arranged closer to the front substrate than the half-transmission, half-reflection layer; a backlight arranged on the back side of the other substrate; and a cholesteric liquid-crystal layer arranged between the half-transmission, half-reflection layer and the backlight, for selectively reflecting light with wavelengths lying between adjacent peak wavelengths in a spectral transmittance characteristic of the color filter layer.
In the typical structure of the liquid-crystal display device according to the present invention, the polarizing plate, phase difference plate, color filter layer, optical phase modulation liquid-crystal layer functioning as a variable retarder layer, selective reflection layer, and cholesteric liquid-crystal layer for selectively reflecting and transmitting the light from the backlight are provided in that order when viewed from the observer side. The cholesteric liquid-crystal layer adapts the wavelength characteristic of the backlight to the spectral transmittance characteristic of the color filter layer. Specifically, the cholesteric liquid-crystal layer selectively reflects and cuts off wavelengths between peak wavelengths of the color filter layer, thereby adjusting the emission spectrum of the backlight.
The foregoing object is further accomplished by providing a liquid-crystal display device comprising: a front substrate and a back substrate which are arranged to face each other and on an inner surface of each of which a liquid-crystal driving electrode is provided; a liquid-crystal layer sandwiched between the front substrate and the back substrate, for modulating the phase of incident light according to an applied voltage; a phase difference plate and a polarizing plate with a polarizing axis which are provided in that order on an outer surface of one of the front and back substrates; a selective reflection layer which is arranged on the other substrate and which reflects a first circularly polarized light of incident light and transmits a second circularly polarized light rotating in the opposite direction to that of the first circularly polarized light; a first color filter layer arranged closer to the front substrate than the selective reflection layer; a backlight arranged on the back side of the back substrate; and a band-pass filter arranged closer to the backlight than the selective reflection layer.
When the liquid-crystal display device functions as the reflective type, the incident light passes through the first color filter layer twice, the spectral transmittance characteristic of the first color filter layer is so set that the light passed through twice is colored in the desired color. Therefore, the spectral transmittance characteristic of the first color filter layer becomes a relatively wide band characteristic.
When the liquid-crystal display device functions as the transmission type, because the light from the backlight passes through the first color filter layer only once, a display characteristic with the brightness and color density similar to those of a conventional transmission color liquid-crystal display device can be obtained by causing the light to pass through the band-pass filter to narrow the band of the light before the light enters the first color filter.
An interference filter or a second color filter layer composed of a color absorption filter may be used as the band-pass filter. A dielectric multilayer film constructed by staking dielectrics one on top of another may be used as the interference filter. A filter obtained by adding pigment or dye to an organic medium may be used as the color absorption filter.
When the selective reflection layer is formed on the inner surface of the back substrate and the color absorption filter is placed under the selective reflection layer, this prevents the parallax due to the thickness of the substrate, which prevents the color density from decreasing due to color shift.
When the second color filter layer is provided on the array substrate with active elements, such as thin-film transistors, the pixel electrodes are formed above the scanning lines, signal lines, and thin-film transistors. Therefore, the second color filter layer is also used as an interlayer insulating film, which realizes a high numerical aperture.
Furthermore, when pigment is dispersed throughout or mixed into the selective reflection layer made of cholesteric liquid-crystal polymers, the selective reflection layer can function as the second color filter layer. This makes it possible to cause a single layer to function as both the selective reflection layer and second color filter layer, which reduces the number of layers in the liquid-crystal display device on the whole.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.